Tuning the magnetic properties of Co nanoparticles by Pt capping

Abstract

We show that by capping Co nanoparticles with small amounts of Pt strong
changes of the magnetic properties can be induced. The Co nanoparticles have a
mean diameter of 2.7 nm. From magnetometry measurements we find that for zero
and for small amounts of Pt (nominal thickness t(Pt) < 0.7 nm) the
nanoparticles behave superparamagnetic like. With increasing t(Pt) the blocking
temperature is enhanced from 16 up to 108 K. Capping with Pd yields comparable
results. However, for values t(Pt) > 1 nm a strongly coupled state is
encountered resembling a ferromagnet with a T_c approx. 400